On Mon, Aug 12, 2019 at 7:36 PM Bruno Marchal <marc...@ulb.ac.be> wrote:
> On 12 Aug 2019, at 04:06, Bruce Kellett <bhkellet...@gmail.com> wrote: > > > If you do not measure which slit the photon went through, then the > superposition of slits is not broken by decoherence. > > Decoherence break things only if there is a collapse. > That is simply incorrect. I refer you again to Zurek, who works in a basically Everettian framework, but he stresses the importance of environmental induced superselection (einselection) in producing the preferred pointer basis. This then breaks things, in the sense that no other basis is stable against decoherence, and other sets of basis vectors rapidly (in times of the order of femtoseconds) collapse on to the preferred pointer states. This is the basis of the emergence of the classical world from the quantum substrate. And this occurs in Everett's relative state approach just as much as in a Copenhagen-like collapse models. Without collapse, even if I measure which slit the photon went through, the > two terms of the superposition continue to exist, describing me seeing both > outcomes, and both me feel like if there has been a collapse, > No, that is not really true. Complementarity plays a role. Measurement of which slit the photon went through is incompatible with the effective momentum measurement that gives interference at the screen. That is essentially why the slit measurement destroys the possibility of interference. There is an incompatibility between the measurements -- basically related to the non-commutation of position and momentum operators and the Heisenberg uncertainty principle. and that decoherence is physical real, but that illusion is explained by > the formalism, in a manner similar to the WM duplication: it is just first > person indeterminacy, not in a self-duplication, but in a self entanglement. > Not really true, either. Decoherence, the formation of a stable pointer basis, and the like, are all essential for the emergence of the classical from the quantum, and the formation of objective physical states. This is the operation of Zurek's Quantum Darwinism -- the environment acting as witness. So this is third person objective physics -- it is not first person indeterminacy. Bruce -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/CAFxXSLRBghQR4Z1MKLdSQOGGpte7jnOjvt_vtxQ_Pohx9MDCZQ%40mail.gmail.com.
